Is this a fair comparison? Of course not, but, wouldn't you like to know just how big a difference there really is? Wouldn't you like to know just what you're giving up when you leave that clunky DSLR at home?
Let's review a few basics. Pixel (or megapixel) count is an over-hyped number that is but one of many factors that influence image quality. The final image is affected by lens quality, focus accuracy, sensor size, sensor quality, in-camera image processing, pixel size--and--the skill and technique of the photographer. When all other things are equal (which in real-life they rarely are) more pixels can be better. But when camera makers try to cram more pixels into a small sensor, those pixels are physically smaller, and that means fewer photons fall on them, and that usually means more noise, which looks like multi-colored confetti that isn't supposed to be there.
These two cameras are very different. The iPhone 4s with a protective case weighs just 6 ounces. The Nikon with lens weighs about 40 ounces. The iPhone can slip into the pockets of your tightest jeans, the Nikon will hardly fit in any pocket. The iPhone 4s has 8 megapixels in a tiny sensor, the Nikon has 16 megapixels in a mid-size sensor. Each pixel in the Nikon is almost twice the size of the pixels in the iPhone. But it's not all downside for small sensors. They need shorter focal-length lenses that are much smaller, lighter and easier to manufacture. That shortened focal length also means they have more depth of field, meaning that objects or people in front of and in back of where you focused are sharper. That can be either a good or bad thing depending on the picture.
Now to the comparison. I set both cameras to "auto everything" (actually the iPhone is that way whether you like it or not.) All of the pictures were taken handheld, which is generally not the best for scientific comparisons of sharpness but the way most pictures are taken in the real world. I did no manipulation or sharpening in Photoshop except for resizing. The crops of the iPhone pictures are at 100 percent, which approximates what you would see taking a close look at an 8x10 inch print. The Nikon crops are at 75 percent (400 pixels in the file equals 300 pixels on your screen, because the Nikon's sensor has more pixels than the iPhones, and so doesn't need to be enlarged as much for that same 8x10 print. On the top are iPhone pictures, right underneath the Nikon pictures.
Both pictures are quite pleasing. The iPhone (top) picture's white balance is too warm--both the house and concrete driveway should be neutral gray. The Nikon has slightly more shadow detail, and the shadows are less milky than the iPhone's.
This picture, taken in soft light, was not very challenging for either camera. The iPhone picture (top)is slightly warmer and more saturated; the Nikon is more accurate. Notice that the woman's eyes are lighter in the Nikon picture. But both are very acceptable.
The Nikon image (bottom) is sharper, but there isn't a huge difference. Again, print or projections larger than 8x10 would show a larger difference.
This challenging scene with high contrast (and thus high dynamic range) really showed the greatest difference between the two cameras. From the mid-tone grass you can see that the exposures are almost identical. But look at the huge difference in the brighter parts of the seat. The iPhone couldn't handle those parts and they faded to almost white. The Nikon (bottom) accurately recorded the highly saturated colors even in the brightest spots,
What does all this mean?
I've been a professional photographer for 40 years, and I'm really picky about quality, especially color quality. (In fact, a veteran printer told me I was the pickiest and most color-discerning printing customer he had ever had. He thought it was an insult; I took it as a complement.) Here are my conclusions--
1. The iPhone camera is amazing. The makers of low to mid-level point-and-shoot cameras should be scared, because that market will soon be dead.
2. For most casual shooters who take pictures for Facebook, for family memories or to give to their friends or put on their websites, the iPhone will be just fine for most of their pictures. I'll use my iPhone for these type pictures, too.
3. The best camera is the one you have with you. The fact that the iPhone takes pictures this good in a small package that most people will carry with them most of the time will revolutionize still and video captures. We will see more pictures of more events and of better quality than ever before. Already the iPhone 4s is the camera most used by Flickr contributors.
4. Serious amateurs and professionals will still be lugging around their DSLRs and heavy lenses. Virtually all of the pictures on this website would have been impossible to take with the iPhone. The interchangeable lenses, overall image quality, low light capability, faster shooting and focusing, dynamic range, ruggedness and the limited depth of field when needed all continue to make DSLRs an essential tool...for now.